You have to have done seasonal work like fruit picking, tree planting, fishing or mining for at least three months in one of the following areas (
http://www.immi.gov.au/visitors/work...postcodes.htm), you can apply for a second Working Holiday Maker visa.
I don't think the Dept of Immigration considers cafe work to be seasonal, although in some parts of the country it could be considered seasonal.
See
www.immi.gov.au/media/fact-sheets/49whm.htm#a for more information.